2 Replies Latest reply on Sep 14, 2020 3:04 PM by JaKu_4775896

    Cascading 2 CY7C65642 Hubs


      Hi all,


      I have two cy7c65642 hubs arranged in a cascaded manner. The downstream hub is not able to connect in both Windows and Ubuntu, with the following messages respectively: "not enough power on the USB hub" and "can't connect bus-powered hub to this port".


      The hubs are configured for bus power, i.e. SELFPWR pins pulled low.


      I couldn't find anything in the datasheet explicitly requiring self-power for cascading hubs. Is this required? As such, will pulling the SELFPWR pins on both hubs high fix this issue?


      NB: I connected the supply line to an external power supply, and measured current was < 200 mA

      The default max power of 100mA was also increased to 500 mA in the EEPROM config.



        • 1. Re: Cascading 2 CY7C65642 Hubs



          The error messages that appear are due to power limitation on bus-powered hubs as it is not recommended to connect two bus-powered hubs in a cascaded manner. The reason for this is that the maximum power available on each port of a bus-powered hub is 100mA, but when you connect another hub to a downstream port of the first hub, 100mA is not sufficient to power the second hub and its downstream ports. Please refer to section 2.2 of the App Note for a more detailed explanation- https://www.cypress.com/file/122726/download


          As you mentioned, setting the powering mode to self-powered using the SELFPWR pins will fix the issue as both the hubs wont be drawing any power from the host downstream port.

          Please also note that the EEPROM configuration maximum power value is that required by the hub only i.e. what will appear in the hub configuration descriptor and wont include the power requirement of the downstream devices.


          Best Regards,

          • 2. Re: Cascading 2 CY7C65642 Hubs

            Thanks for the feedback. I will make those changes and report back